Geothermal Energy
* Could it be the ultimate answer to our energy needs?
* Could it be the ultimate answer to winter heating?
* Could it be the ultimate answer to transportation energy
* Could it be the ultimate answer to the CO2 problem?
* Could it bring those billions of energy $ back to the U.S. economy?
* Could it solve the global warming scare?
* Can we develop new and improve existing technologies soon enough?
Geothermal Energy Facts
Initial cost of a geothermal power plant is about the same as for a coal fired plant of the same capacity.
Geothermal power plants:
1. Burn no fossil fuel and emit no carbon dioxide.
2. Can be located and utilized in about 60% of the continental U.S.
3. Are environmentally better than virtually any other form of energy.
4. Can even be used to sequester carbon dioxide.
5. Could be a huge economic bonanza for the U.S.
6. Are already a reality using improving technology.
7. Are really in their infancy compared to other energy plants.
(That means geothermal technology has a lot of room to expand and improve greatly.)
Geothermal power plant in the Imperial Valley, California.
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Geothermal Power Plants
There are three geothermal power plant technologies being used to convert hydrothermal fluids to electricity. The conversion technologies are dry steam, flash, and binary cycle. The type of conversion used depends on the state of the fluid (whether steam or water) and its temperature. Dry steam power plants systems were the first type of geothermal power generation plants built. They use the steam from the geothermal reservoir as it comes from wells, and route it directly through turbine/generator units to produce electricity. Flash steam plants are the most common type of geothermal power generation plants in operation today. They use water at temperatures greater than 360°F (182°C) that is pumped under high pressure to the generation equipment at the surface. Binary cycle geothermal power generation plants differ from Dry Steam and Flash Steam systems in that the water or steam from the geothermal reservoir never comes in contact with the turbine/generator units.
U.S. Geothermal Power Plants include: Casa Diablo, Navy 1, The Geysers, Hawaii, Honey Lake Imperial Valley, Nevada, and Utah
Dry steam power plants at The Geysers in California.
There are three geothermal power plant technologies being used to convert hydrothermal fluids to electricity. The conversion technologies are dry steam, flash, and binary cycle. The type of conversion used depends on the state of the fluid (whether steam or water) and its temperature. Dry steam power plants systems were the first type of geothermal power generation plants built. They use the steam from the geothermal reservoir as it comes from wells, and route it directly through turbine/generator units to produce electricity. Flash steam plants are the most common type of geothermal power generation plants in operation today. They use water at temperatures greater than 360°F (182°C) that is pumped under high pressure to the generation equipment at the surface. Binary cycle geothermal power generation plants differ from Dry Steam and Flash Steam systems in that the water or steam from the geothermal reservoir never comes in contact with the turbine/generator units.
U.S. Geothermal Power Plants include: Casa Diablo, Navy 1, The Geysers, Hawaii, Honey Lake Imperial Valley, Nevada, and Utah
Dry steam power plants at The Geysers in California.
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Dry Steam Power Plants
Dry Steam plants use hydrothermal fluids that are primarily steam. The steam goes directly to a turbine, which drives a generator that produces electricity. The steam eliminates the need to burn fossil fuels to run the turbine. (Also eliminating the need to transport and store fuels!) This is the oldest type of geothermal power plant. It was first used at Lardarello in Italy in 1904, and is still very effective. Steam technology is used today at The Geysers in northern California, the world's largest single source of geothermal power. These plants emit only excess steam and very minor amounts of gases.
Dry Steam plants use hydrothermal fluids that are primarily steam. The steam goes directly to a turbine, which drives a generator that produces electricity. The steam eliminates the need to burn fossil fuels to run the turbine. (Also eliminating the need to transport and store fuels!) This is the oldest type of geothermal power plant. It was first used at Lardarello in Italy in 1904, and is still very effective. Steam technology is used today at The Geysers in northern California, the world's largest single source of geothermal power. These plants emit only excess steam and very minor amounts of gases.
Illustration of a Dry Steam Power Plant
Operation - Geothermal steam comes up from the reservoir through a production well. The steam spins a turbine, which in turn spins a generator that creates electricity. Excess steam condenses to water, which is put back into the reservoir via an injection well.
Flash Steam Power Plants
Hydrothermal fluids above 360°F (182°C) can be used in flash plants to make electricity. Fluid is sprayed into a tank held at a much lower pressure than the fluid, causing some of the fluid to rapidly vaporize, or "flash." The vapor then drives a turbine, which drives a generator. If any liquid remains in the tank, it can be flashed again in a second tank to extract even more energy.
Illustration of a Flash Steam Power Plant
Pressurized geothermal hot water comes up from the reservoir through a production well. The water enters a flash tank where it depressurizes and flashes to steam. The steam then spins the turbine, which in turn spins a generator that creates electricity. Excess steam condenses to water, which is put back into the reservoir via an injection well.
Binary-Cycle Power Plants
Most geothermal areas contain moderate-temperature water (below 400°F). Energy is extracted from these fluids in binary-cycle power plants. Hot geothermal fluid and a secondary (hence, "binary") fluid with a much lower boiling point than water pass through a heat exchanger. Heat from the geothermal fluid causes the secondary fluid to flash to vapor, which then drives the turbines. Because this is a closed-loop system, virtually nothing is emitted to the atmosphere. Moderate-temperature water is by far the more common geothermal resource, and most geothermal power plants in the future will be binary-cycle plants.
Illustration of a Binary Cycle Power Plant.
Geothermal hot water comes up from the reservoir through a production well. The hot water passes by a heat exchanger that is connected to a tank containing a secondary hydrocarbon fluid. The hot water heats the fluid, which turns to vapor. The vapor spins a turbine, which in turn spins a generator that creates electricity. The hot water continues back into the reservoir via an injection well. This closed-loop system can be used where the water resource is too cool for direct use in turbines.
The Future of Geothermal Electricity
Steam and hot water reservoirs are just a small part of the geothermal resource. The Earth's magma and hot dry rock will provide cheap, clean, and almost unlimited energy as soon as we develop the technology to use them. In the meantime, because they're so abundant, moderate-temperature sites running binary-cycle power plants will be the most common electricity producers.
Before geothermal electricity can be considered a key element of the U.S. energy infrastructure, it must become cost-competitive with traditional forms of energy. The U.S. Department of Energy is working with the geothermal industry to achieve $0.03 to $0.05 per kilowatt-hour. We believe the result will be about 15,000 megawatts of new capacity within the next decade.
DOE Support
The U.S. Department of Energy recognizes the strategic value of geothermal electricity, and supports its development in several ways through its Geothermal Technology Development Program. First, it works with Congress to ensure support for geothermal energy and renewables in general. Second, it sponsors millions of dollars in research and development at national laboratories and universities. Investigators are working on issues in exploration, geochemistry, drilling, resource usage, and equipment operation. Third, through its GeoPowering the West initiative, it works with state and local officials and other stakeholders to identify and overcome regulatory and institutional barriers to geothermal power development.
This is from: http://www1.eere.energy.gov/geothermal/powerplants.html
In many areas of the U.S. where geothermal energy high enough for power plant use is too deep for economic use, it is still hot enough to use for heating homes, offices and other commercial and government buildings. With heating being a major user of fossil fuel energy, especially in the northern areas of the country, plants and systems to distribute geothermal heat could be one practical way to lower substantially our use of fossil fuels. Systems to distribute heat through insulated pipes to homes and buildings throughout a city would cost little more than those already in use for natural gas. In some areas of the U.S. exhaust steam from power plants is used in just such a manner for heat in cold weather. In some places it is even used to heat sidewalks and streets to keep them free from ice and snow.
For more information on the practical use of geothermal energy, go to: http://www1.eere.energy.gov/geothermal/index.html
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Article From http://technology.newscientist.com/article/dn10478
18:00 08 November 2006 NewScientist.com news service Tom Simonite
Pumping carbon dioxide through hot rocks could simultaneously generate power and mop up the greenhouse gases produced by fossil fuel power stations, according to a new study.
Harnessing geothermal power involves extracting heat from beneath the surface of the Earth. Normally, this means pumping water down through hot rocks and extracting it again. But the new analysis suggests carbon dioxide could extract heat from rocks more efficiently than water.
Karsten Pruess, a hydro-geologist at Lawrence Berkeley Laboratory in the US, carried out the study and says carbon dioxide could theoretically boost the amount of energy produced by hydrothermal plants by 50% or more. At the same time, Pruess calculates that the technique could be used to dispose of the carbon dioxide produced by conventional power plants, which contribute to global warming.
Pruess used the Soultz hydrothermal plant, in northwest France, as a model to test the idea, which was originally proposed by Donald Brown of Los Alamos National Laboratory, US, in 2000. The Soultz plant pumps water into the ground through a single borehole and uses water heated to around 200°C, recovered via another borehole, to drive turbines and generate electricity.
Harebrained idea?
Pruess calculated that the plant would perform more efficiently if carbon dioxide was used instead of water. "Initially I thought this was the most harebrained idea I had ever heard," he told New Scientist. "But the more I looked the more I liked it." Pruess discovered that using carbon dioxide to drive turbines and generate electricity, either directly or indirectly through the use of steam, could produce 50% more energy.
Although carbon dioxide cannot carry as much heat as water, it could boost efficiency because it can move through the plant's system much more quickly. "Carbon dioxide is to water what water is to honey," Pruess explains. "It is much less viscous."
In addition, less energy would be required to drive carbon dioxide through the system in the first place. Hot gas in the exit borehole would be less dense than colder gas in the entry borehole, and this density difference would help drive gas through the rock with little need for pumping. Furthermore, because some gas would leak into the rock, such a plant could be used to store carbon dioxide, Pruess says.
Storage trials
Carbon storage trials in the North Sea and Algeria have involved sequestering around a million tonnes of carbon – the annual output from a 150MegaWatt (MW) coal power station – beneath ground. Pruess says that, over a year, a small geothermal plant could store the same amount of carbon while also generating 50MW.
Pruess bases his calculations on the assumption that the same amount of carbon dioxide would leak into the rock as does water in existing geothermal plants. But he plans to carry out chemical tests that should help reveal whether this is really the case when hot pressurised carbon dioxide is pumped through underground rock.
Robert Pine, an expert on hydrothermal power at the Camborne School of Mines in the UK, says using carbon dioxide system is a novel idea. "But leakage could be a serious issue," he told New Scientist. "All carbon sequestration projects I am aware of use old gas or oil fields that function as geological traps."
While carbon dioxide is unlikely to escape from such traps, rock fractures, which are common in regions used for hydrothermal operations, could allow gas to leak out, Pine warns. "Using gas fields might be better, but because they aren't very hot you would have to go very deep to get to the heat."
There are problems to solve and challenges to face in every new technological advancement. One would better ask the question, How do we solve this problem or meet this challenge? than Can the problem be solved or the challenge met?
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